Fruits, vegetables and other plant foods are packed with healthy compounds known as phytochemicals, in addition to vitamins, minerals and fiber. From anthocyanins (the red pigment in strawberries and cherries) to allylic sulfides (responsible for the pungent flavor of garlic and onions), these phytochemicals may be responsible for some of the disease-preventing effects of fruits and vegetables.
Phytochemicals have no nutritive value, but they may have positive effects on the body over the long term. Possible beneficial effects of phytochemicals include inhibiting tumor formation, preventing blood clots, blocking the cancer-promoting effect of certain hormones and lowering cholesterol levels.
Phytochemicals may be important in disease prevention, either on their own or in combination with antioxidants or other food components, such as fiber. This vast number of compounds in fruits, vegetables, grains and legumes makes it nearly impossible for supplements to substitute for a healthy diet. Here are six phytochemicals and where you can find them in food.
1. Allylic sulfides. Found in onions and garlic, these substances may enhance immune function, help the body excrete cancer-causing compounds, and interfere with the development of tumors.
2. Flavonoids. These compounds may extend the life of vitamin C, inhibit tumor development, prevent the oxidation of LDL (bad) cholesterol, and control inflammation. Flavonoids are found in a variety of fruits and vegetables as well as in red wine, red and purple grape juice, and green and black tea.
3. Indoles, isothiocyanates, and sulforaphane. Broccoli, kale, Brussels sprouts and other members of the cabbage family (known as cruciferous vegetables) contain a potent substance called sulforaphane that stimulates cells to produce cancer-fighting enzymes. Indoles and isothiocyanates, two compounds that also are present in cruciferous vegetables, have been found to act in a similar manner.
4. Phenolic acids. Ellagic acid, ferulic acid, and other phenolic acids may prevent damage to DNA. They are found in strawberries, raspberries, tomatoes, citrus fruits, whole grains and nuts.
5. Phytoestrogens. Phytoestrogens are plant substances that are converted to estrogen-like compounds by bacteria in the intestine. They are present in many plant foods, especially soybeans and soy products such as tofu and soy milk. Lignans and isoflavones are examples of phytoestrogens.
Some research has suggested that these compounds protect against hormone-dependent cancers of the breast, uterus and prostate by blocking the actions of certain hormones that stimulate tumor growth. Some reports suggest that women who eat a lot of soy products have fewer hot flashes associated with menopause, and soy products may moderately lower blood cholesterol levels. However, these findings have not been confirmed by other studies. The latest review of research suggests that phytoestrogens (and other components of soy) do not lower the risk of hormone-dependent cancers, reduce the frequency of hot flashes or significantly lower cholesterol levels.
Soy foods are not recommended for survivors of hormone-positive breast cancer because the phytoestrogens in them may fuel the growth of certain cancer cells. But for the majority of people, soy-containing products are still good for your health because they contain fiber, protein and many important vitamins and minerals.
6. Saponins. These sugar-like compounds have an antibacterial effect. Saponins may strengthen the immune system, prevent microbial and fungal infections and fight viruses. They are found in potatoes, tomatoes, legumes, oats and spinach.
Boost your phytochemicals
Follow these tips to increase the phytochemicals in your diet.
• Consume a plant-based diet. Try to eat nine servings of fruits and vegetables a day (including 3 cups of legumes a week) and six servings of grain products each day. Vary the choices to get a wide range of phytochemicals, focusing on dark green vegetables, red and orange fruits and vegetables, and whole grains.
• Season foods with herbs and spices. These seasonings also contain phytochemicals. Try using garlic, shallots, ginger, basil, oregano, parsley, rosemary, cumin, curry powder, cayenne pepper, red chili pepper and cinnamon, to name a few.
• Incorporate soy products into your diet. Tofu, soy protein, soy milk, soy flour, soy butter and edamame (edible green soybeans) can all be included in your diet as long as you have not been advised to avoid them.
Tofu and other soy products are mild tasting and pick up the flavor of the foods they are cooked with. Tofu can be stir-fried with vegetables or added to soups. Soy flour can be substituted for up to one quarter of the flour in baking recipes, and soy butter can be spread on bread in place of peanut butter.